Can your body go into starvation mode after 12 hours of not eating and only drinking water?

Starvation mode is not the way to lose weight. You gain it ALL back and then some when you start eating again one reason being because your metabolism will be thrown off.
Plus if you don't know how to break 'a fast' properly then you could get really ill.
The only way to properly lose weight is learn what foods your body burns calories and fat best.
With starvation mode, your body believes it's about to starve, the first thing it does is shut down its fat-burners to preserve fuel (fat) so you actually retain the fat.

First no it does not, but starvation is not a weight loss, in fact you will normally gain the weight back shortly after. In fact you often gain more of it back.

Can your body go into starvation mode after 12 hours of not eating and only drinking water?
This is the second thread I have seen you post regarding this situation. You really need to go see a doctor. For some reason you are made to believe that starving yourself will salve the problem. I am sorry to say it will not. You need to exercise and eat right. This is the only healthy option that you have. You are really killing you body by starving yourself.